Casio CZ/ VZ/ FZ - Pro Series

I would start as usually:
- check if all fuses are OK (if there are some)
- check PSU voltages if all are on the spec
- if necessary change electrolytic caps in PSU
- check, clean and reseat all connectors
- reseat all chips in sockets (OS Eprom for example ?)

If this doesn't help, then there's more problems somewhere in hardware  
or software which would need more checking...

Daniel Forro

On 11 Dec, 2014, at 4:59 AM, db0451@... [CZsynth] wrote:

>
>
> Hello all,
>
> Looking for advice from FZ-10M owners. I have bought one that needs  
> repair - does not start, only showing a screen light and (sometimes)  
> 2 red LEDs.
>
> Not got much in the way of diagnostic equipment but am happy to try  
> if I get plausible suggestions. Service manual for FZ-1 only  
> describes the diagnostic program IF it loads in the first place, but  
> I don't seem to get that far.
>
> Doubt it's just the LCD screen, but to check, how would I go about  
> testing buttons or sound without being able to see what the screen  
> says? Anything simple that will produce a sound or change some LEDs  
> if the whole thing isn't busted.
>
> Otherwise, yeah, hopefully someone knows that pattern of failure,  
> and can suggest what needs replaced, tested, etc.
>
> Thanks in advance, really hope I can get this fixed and get those  
> filters blasting!
>
> DB

On Fri, Dec 12, 2014 at 03:55:28PM -0800, db0451@... [CZsynth] wrote:
> Hi Daniel,
> 
> Thanks for the ideas. Indeed, it might be a PSU problem. For the full latest details, please see my thread on Vintage Synth Explorer: http://www.vintagesynth.com/forum/viewtopic.php?f=5&t=78014 http://www.vintagesynth.com/forum/viewtopic.php?f=5&t=78014  
> But in brief, the cable at the back of the FDD does not supply +12 V - only 0.05 V, even if the synth is powered off! And the +12 V supply seems to come through the fuse F4, rectifier S1WBA10, a bunch of transistors and other things, and finally an electrolytic capacitor. While I could unscrew the PSU and replace everything, it would be nice to have a better idea of what to test - and which things are worth replacing. :-)

Could be a bunch of things.  Check that you've got AC coming into the 12V rectifier and DC coming out.  There's then a fairly simple linear regulator, where a likely suspect would be the pass transistor.

In order I'd check that there's DC present across the first smoothing capacitor just after the rectifier, and if there isn't I'd check for AC from the appropriate transformer winding.  Check the fuse is okay and the clips are clean and secure (they corrode).  If there's AC going into the rectifier but no output, it's probably faulty in which case you desolder it and check it.  The most likely thing is that it's failed short circuit, in which case you really should replace the smoothing capacitor that follows it too, which will have been given a hard time by all that AC.

See if you get unregulated DC at the input to the regulator *first*.  You should see about 16V across that first smoothing cap.

-- 
Gordonjcp MM0YEQ